Upper limit for the effect of elastic bending stress on the saturation magnetization of $\mathrm{L}{\mathrm{a}}_{0.8}\mathrm{S}{\mathrm{r}}_{0.2}\mathrm{Mn}{\mathrm{O}}_3$

Using polarized neutron reflectometry, we measured the influence of elastic bending stress on the magnetization depth profile of a $\mathrm{L}{\mathrm{a}}_{0.8}\mathrm{S}{\mathrm{r}}_{0.2}\mathrm{Mn}{\mathrm{O}}_3$ (LSMO) epitaxial film grown on a $\mathrm{SrTi}{\mathrm{O}}_3$ substrate. The elastic bending strain of $\pm 0.03\%$ has no obvious effect on the magnetization depth profile at saturation. This result is in stark contrast to that of $(\mathrm{L}{\mathrm{a}}_{1-x}\mathrm{P}{\mathrm{r}}_x{)}_{1-y}\mathrm{C}{\mathrm{a}}_y\mathrm{Mn}{\mathrm{O}}_3$ (LPCMO) films for which strain of $\pm 0.01\%$ produced dramatic changes in the magnetization profile and Curie temperature. We attribute the difference between the influence of strain on the saturation magnetization in LSMO (weak or none) and LPCMO (strong) to a difference in the ability of LSMO (weak or none) and LPCMO (strong) to phase separate. Our observation provides an upper limit of tuning LSMO saturation magnetization via elastic strain effect.

Figure 1

(a) X-ray diffraction $\theta /2\theta$ scan for LSMO/STO film. Inset: $\theta /2\theta$ scan around STO (002) and LSMO (002) peaks. (b) Reciprocal space map around STO (103) and LSMO (103) reflections. (c) X-ray reflectivity curve normalized to $R_F$ and the corresponding fit for LSMO/STO film. Inset: X-ray scattering length density depth profile obtained from the best fit. (d) STEM $Z$-contrast image of a thinner (34 nm) LSMO/STO film sample taken down the (110) zone axis. Inset: A low-magnification image. (e) Normalized, integrated EELS profiles measured along the growth direction obtained from the $\mathrm{Ti}{\mathrm{L}}_{2,3},\mathrm{O}\mathrm{K}, \mathrm{Mn}{\mathrm{L}}_{2,3}$, La ${\mathrm{M}}_{4,5}$, and Sr ${\mathrm{L}}_{2,3}$ absorption edges. Data acquired in a Nion UltraSTEM200, operated at 200 kV, equipped with a fifth-order aberration corrector and a Gatan Enfinium spectrometer.

Figure 2

(a) Temperature dependence of the magnetization. Lower inset: The corresponding derivative curve. Upper inset: M-H curve at 50 K and $\pm 10\mathrm{kOe}$. (b) Temperature dependence of the resistivity at different thermal and field conditions.

Figure 3

(a)–(c) Polarized neutron reflectivity normalized to $R_F$ for three values of bending strain and the corresponding fits. (d) Obtained nuclear scattering length density depth profile. (e) Obtained magnetization depth profiles for three bending cases.

Figure 4

Square of the magnetization for the LSMO film bulk region (red), LSMO interfacial region (blue), LPCMO film bulk region at 78 K (green), and at 20 K (purple) vs applied bending strain. The symbols represent the optimal values. The shaded regions represent the confidence of the values.